Dynamoelectric machines are machines that generate electric power or use electric power. Common types of dynamoelectric machines are alternators, generators, and electric motors.
Electric motors are used in a wide variety of applications involving power tools such as drills, saws, sanding and grinding devices, yard tools such as edgers and trimmers, just to name a few such tools. These devices all make use of electric motors having an armature and a field, such as a stator. The armature is typically formed from a lamination stack or core around which a plurality of windings of magnet wires are wound. The lamination stack is formed to have a plurality of poles around which the magnet wires are wound. In this regard, the lamination stack may be formed with a plurality of slots in which the magnet wires are wound. Insulators are typically provided between the magnet wires and the lamination stack. Magnet wires, as that term is commonly understood, are wires of the type conventionally used to wind coils in electric machines, such as armatures and stators. The magnet wires are coupled at their ends to a commutator, such as to tangs when the commutator is a tang type commutator, disposed on an armature shaft extending coaxially through the lamination stack.
The stator is also typically formed from a lamination stack around which a plurality of windings of magnet wires are wound. The ends of the magnet wires typically have terminals affixed that are then coupled to a source of electrical power. The lamination stack is formed to have a plurality of poles around which the magnet wires are wound. In this regard, the lamination stack may be formed with a plurality of slots in which the magnet wires are wound. Insulators are typically provided between the magnet wires and the lamination stack.
In the manufacturing process for the armature described above, once the magnet wires have been secured to the commutator, a “trickle” resin is applied over the magnet wires and over the ends of the magnet wires where they attach to tangs associated with the commutator. The process of applying the trickle resin is a somewhat difficult process to manage to obtain consistent results. It also has a number of drawbacks, not the least of which is the cost and difficulty of performing it with reliable, consistent results.
Initially, the trickle process requires the use of a relatively large and expensive oven to carefully preheat the partially assembled armatures to relatively precise temperatures before the trickle resin can be applied. The temperature of the trickle resin also needs to be carefully controlled to achieve satisfactory flow of the resin through the slots in the lamination stack of the armature. It has proven to be extremely difficult to achieve consistent, complete flow of the trickle resin through the slots in the lamination stack. As such, it is difficult to achieve good flow in between the magnet wires with the trickle resin. A cooling period must then be allowed during which air is typically forced over the armatures to cool them before the next manufacturing step is taken. Further complicating the manufacturing process is that the trickle resin typically has a short shelf life, and therefore must be used within a relatively short period of time. The manufacturing process for making wound stators may involve a similar trickle resin process.
Referring to FIG. 1, there is illustrated a prior art armature 10 made in accordance with a conventional manufacturing process incorporating the trickle resin application steps described hereinbefore. The armature 10 incorporates a lamination stack 12 having a plurality of longitudinal slots 14 disposed circumferentially therearound. Wound within the slots 14 is a large plurality of magnet wires 16 forming coils. An armature shaft 18 extends coaxially through the lamination stack 12 and includes a commutator 20. An independently formed plastic fan 22 is secured, typically by adhesives, to the lamination stack 12. The fan 22 typically includes a plurality of legs 24 which project into the slots 14, thus taking up space which would more preferably be occupied by the magnet wires 16. Trickle resin 26 is applied over the magnet wires 16, in the slots 14, and also at the tangs 25 where the ends 16a of the magnet wires 16 attach to the commutator 20.
Abrasive particles are drawn in and over the armature by the armature's fan, particularly when the armature is used in tools such as grinders and sanders. As shown particularly in FIG. 2, the air flow, shown by arrows 30, impinges magnet wires 16 of end coils 17 (the portion of the coils of magnet wires that extend around the ends of the lamination stack 12 between the slots 14 in the lamination stack 12). The air flow 30 contains abrasive particles and the impingement of these abrasive particles on magnet wires 16 can wear away the insulation of magnet wires 16.
With present day manufacturing techniques, an additional or secondary operation is often required to protect the armature (and specifically the magnet wires) from the abrasive particles. Such secondary operations include a coating of higher viscosity trickle resin, an epoxy coating, or wrapping the wires, such as with cotton, string or the like. This serves to further increase the manufacturing cost and complexity of the armature.
Still another drawback with the trickle process is the relatively high number of armatures which are often rejected because of problems encountered during the process of applying the trickle resin to an otherwise properly constructed armature. Such problems can include contamination of the commutator of the armature by the trickle resin during the application process, as well as uneven flow of the trickle resin if the pump supplying the resin becomes momentarily clogged. Accordingly, the difficulty in controlling the trickle resin application process produces a relatively large scrap rate which further adds to the manufacturing cost of electric motors.
Slot insulators and end spiders of armatures have been formed by insert molding the armature shaft and lamination stack in plastic. FIG. 3 shows such a prior art armature 40 having a lamination stack 42 on a shaft 44. Lamination stack 42 has a plurality of slots 46. The plastic is molded underneath the lamination stack 42 and around shaft 44 to insulate the shaft 44 from the lamination stack 42. The plastic is also molded to form end spiders 48 and molded in slots 46 to form slot liners 50. Slot liners 50 insulate the windings 52 from lamination stack 42 after the windings 52 have been wound in the slots 46 to form coils 54.
The plastic used in molding the prior art armature 40 has been plastic that is not thermally conductive, such as nylon or PPS. This can result in problems in dissipating the heat generated in the coils 54 during the operation of the motor in which armature 40 is used.
Most armatures or rotors used in dynamoelectric machines, such as motors and generators, are dynamically balanced to reduce the vibration force transmitted to the motor housing by way of the bearings. Dynamic balancing requires that material be added to or removed from the ends of the armature. The most beneficial places to do this are on planes near to the bearing planes at the largest possible radius. However, for practical reasons, universal motor armatures and permanent magnet motor armatures are usually balanced by selectively removing material from the surface of the iron core (also called the lamination stack).
This balancing process has a number of disadvantages. First, the planes in which the material are removed are located within the length of the lamination stack and thus are relatively distant from the bearing planes where the imbalance forces are transmitted to the rest of the product. Second, removal of material from the motor's active iron core (lamination stack) has a negative effect on performance, particularly, torque ripple. Third, balancing by removing material from the surface of the lamination stack requires that the tooth tops of the lamination stack be thicker than needed for spreading magnetic flux. The thicker tooth tops rob winding space from the slots in the lamination stack in which magnet wires are wound. Fourth, the surface of the lamination stack is not homogenous. It consists of iron at the tooth tops and air or resin in the winding slot area. This non-homogeneity presents a more difficult computation to the dynamic balancing machine that must decide how much material to remove and where to remove it from. Consequently, the dynamic balance machines often must make repetitive corrective passes during which even more iron is removed from the lamination stack, further reducing performance.
Coil stays have typically been used to hold the magnet wires, such as magnet wires 16, in the slots, such as slots 14, in the lamination stack, such as lamination stack 12. FIG. 4 shows one of slots 14 of lamination stack 12 of prior art armature 10 (FIG. 1) disposed between opposed poles 13 of lamination stack 12 and magnet wires 16 wound in slot 14. A slot liner 15, typically made of a paper insulation, is disposed in slot 14 between the magnet wires 16 and walls of lamination stack 12. Magnet wires 16 are retained in slot 14 by a coil stay 19, which is illustratively made of vulcanized fibers that are both electrically and thermally insulative. Such prior art coil stays have certain undesirable characteristics. First, they occupy space that could otherwise be filled with magnet wires 16. Second, the poor thermal conductivity of the coil stay material limits the amount of heat that can be transferred to the surface of lamination stack 12.
As is known, the power of a motor having magnet wires wound in slots of a lamination stack is a function of the current flowing through the magnet wires and the number of turns of magnet wires. A motor having a given output, i.e., 1/10 horsepower, ⅛ horsepower, ¼ horsepower, requires that a certain number of turns of magnet wires that can carry a given current be used. The ability of the magnet wires to carry the given current is a function of the size (diameter) of magnet wires. The size of the magnet wires that must be used to wind the given number of turns of the magnet wires in turn dictates the size of the slots in which they are wound. That is, the slots must be large enough to hold the required number of turns of magnet wires.
If a larger size magnet wire can be used to wind the magnet wires, higher power can be achieved due to the decreased resistance of the larger size magnet wire compared with the smaller size magnet wire. However, using a larger size magnet wire to wind the magnet wires would typically require larger slots to accommodate the required number of turns of the larger size magnet wire, which in turn would require a larger lamination stack. Thus the armature would be larger.
Mains driven power tools, tools driven from power mains such as 120 VAC, are often double-insulated to protect the user from electric shock. Double-insulation requires two separate levels of electrical insulation: functional insulation and protective insulation. Functional insulation electrically insulates conductors from one another and from non-touchable dead-metal parts of the armature. An example of a non-touchable dead metal part is the lamination stack of the armature, such as lamination stack 12 (FIG. 1). The functional insulation system includes the core insulation, magnet wire film, and the resin matrix that bonds the whole together. Core insulation could also consist of epoxy coatings applied by a powder coating process.
The protective insulation consists of an electrically insulative tube or sleeve disposed between the touchable dead-metal shaft, such as shaft 18 (FIG. 1), and the rest of the armature structure. The shaft is considered touchable since it is in conductive contact with exposed conductive parts of the tool, such as a metal gearbox and/or metal spindle or chuck. In order to provide protection at the end of the tool's functional life due to abusive loads and burnout, the protective insulation barrier must have electrical, thermal, and structural properties that are superior to those of the functional insulation system. Therefore, the insulating tube or sleeve is usually constructed of high-temperature, glass reinforced thermosetting resin. Other materials such as ceramic, mica, and composites of these materials could also be used to make the insulating tube or sleeve.